An impregnated type cathode has been proposed to improve electric conduction of an oxide cathode. In this impregnated type cathode, the so-called impregnated dispenser cathode having a porous tungsten which is impregnated with electron emission substance has been dominant in this field. This impregnated dispenser cathode has been described, for instance, in the U.S. Pat. Nos. 4,165,473 and 3,358,178.
However, a method for fabricating an impregnated dispenser cathode has disadvantages in that steps are complicated, and a time of each step is long, so that a fabricating cost is increased. In addition, it has a disadvantage in that electron emission is badly affected by hydrooxides of metals in an emitter composed of barium oxide (BaO) calcium oxide (CaO) alumina (Al.sub.2 O.sub.3), etc., because such oxides are easily changed into hydrooxide in atmosphere during assembly process. The hydrooxides melt and cover a surface of the cathode at evacuating stage at a low temperature of several 100.degree. C.